Can a brand-new iPhone be stored in its box long-term? I purchased an iPhone SE last year but still haven’t opened it. Is it safe to leave an iPhone unopened in its box long-term (at room temperature if that makes a difference) without any negative consequences?

From what I understand, the question

Before putting an iPhone5 into very long-term storage should I fully drain battery

discusses about an iPhone that has already been used (and the inquiry is about placing it in long-term storage), whereas mine is asking about a brand-new iPhone.
As long as you have not charged the battery, leaving the unit in the box for long-term storage should pose no difficulty. Batteries as supplied from the manufacturer are holding about 50% charge, which is the ideal amount of charge for lithium batteries to be left in storage.