"Interlocutor" is a great word!
But it is rarely used and will have most people reaching for a dictionary.
The others are not telephone-specific and also carry other inferences, especially interviewer which suggests that the telephone conversation itself is a formal interview and perhaps rather one-sided.
The two parties on a telephone call are officially called the calling party and the called party , although I have not personally heard this used and may be considered old-fashioned.
If the other person initiated the call, you could refer to them simply as " the caller ", which is more common.
Alternatively, you could just refer to them as " the other party ".
ell.stackexchange.com/users/66325/Astralbee
People often say " the person on the other end ".
We speak of a party on a call or of the parties on a call.
In legalistic contexts, party is the word used for either person (or any person) on a phone call.
ell.stackexchange.com/users/10264/Tᴚoɯɐuo
The formal term used in telecommunications is caller and call recipient.
This text on caller ID shows this usage: caller and [call] recipient
In everyday language, as has been suggested, the person I was talking to, the person called, etc., the call taker, for example.
There is no single term that is commonly used.
ell.stackexchange.com/users/33113/Lambie
None of these are good words for this idea.
"Interlocutor" means someone involved in a conversation of any kind, not necessarily on a telephone.
If you're not worried about that distinction, then it's a valid word.
But it's a very rarely used word.
I haven't taken a survey
but I suspect most English speakers are not familiar with the word and would have to guess its meaning or look it up.
"Interviewer" implies that this conversation is an interview, that is, that someone is being questioned by a reporter for a news story, by a company that is considering hiring him for a job, or something of that sort.
We don't use this word for an ordinary conversation.
"Addressee" is normally used for someone to whom you have sent a letter, not a participant in a verbal conversation.
It can be used in cases where a speaker calls someone out in some way, for example, a teacher picks a student to answer a question.
But this is rather rare and use for a phone conversation would be unusual and possibly confusing.
"Hearer" implies that the person is listening only and not speaking.
The word might be used for someone in a crowd listening to a speech, or someone who overhears a conversation between others.
It is not used for someone who participates in a two-way conversation.
All that said, there is no one word in English to refer to someone participating in a telephone conversation.
We normally use a short phrase, like, "the person I called" or "the person who called me".
Other words to refer to a person may be used, like "the man who called", "that jerk who called", etc.
You can call the person who called, "the caller".
You might think that by analogy to other words you could refer to the person receiving the call as "the callee", but no fluent speaker says that.
If you weren't trying to reach a specific person, like if you called a company, you can say "there person who answered" (or "the woman who answered", etc)
Once the context of a phone call is clear, we usually simply call the person by the same sort of shorthand we use for people in general: "him", "that lady", etc.
ell.stackexchange.com/users/803/Jay
If we know who which side made the call, then " answerer " or " caller " can be applicable.
Otherwise, there are some other answers here.
I will go ahead and submit another one for consideration:
The " phone ".
In some cases, this won't work well.
However, in some situations, referring to the phone is a way that people may describe the conversation.
"What I learned from the phone is..."
"
He got mad and was screaming at the phone."
The phone told him...
The phone is making her angry
In these cases, people will know that you're actually referring to the person on the other side of the phone.
Actually, a more clear term is something like "the person she is talking to", like noted in Lambie's comment to Tᴚoɯɐuo's answer .
There is one common advantage to trying to use " caller ", " answerer ", or referring to the " phone " like as if the phone itself is what is listening or speaking.
That advantage is simply shortness.
You can say any of those faster than " the person on the other side of the phone call ".
If you are looking for a shorter phrase, these terms will sometimes accomplish that goal.
ell.stackexchange.com/users/17653/TOOGAM
What is a proper word for a person who you have telephone talk with?I found the words  interlocutor, interviewer, addressee  and  hearer . What is the best to choose, especially for using in a formal way?
What do we call our conversation partner on the telephone?
ell.stackexchange.com
<word-request>
ell.stackexchange.com/questions/179035
ell.stackexchange.com/users/81713/Gamilato
A telephone conversation partner may be referred to as an interlocutor, a caller/call recipient, or the person on the other end. Interlocutor' is a good formal word to refer to a participant in any conversation (not just on the telephione). 'Caller' and 'call recipient' are the formal terms, and 'caller' is commonly used in general language. "The person on the other end" is a more informal way of saying the same thing. 'Interviewer', 'addressee' and 'hearer' are not normally used to refer to callers or speakers in this context.
Interlocutor' is a good formal word to refer to a participant in any conversation (not just on the telephione). Caller' and 'call recipient' are the formal terms, and 'caller' is commonly used in general language. "The person on the other end" is a more informal way of saying the same thing. Interviewer', 'addressee' and 'hearer' are not normally used to refer to callers or speakers in this context.