iPhone stuck on boot screen My non-jailbroken iPhone 6S Plus (iOS 9.3.5) failed to boot up to the lock screen (stuck in apple logo) after the battery was depleted. Hoping to keep my data intact, I have tried several online suggested solutions such as booting it into safe mode (powering on by pressing the power button + volume up button and holding the only volume up button when the apple logo shows) but to no avail.

I looked at several other solutions such as creating a no erase ipsw but am unsure if this is a safe solution (eg. no malware, will not further damage the phone, bricking the phone). 

Has anyone tried this solution or has any other solutions I could try? Really hoping to keep my data. Thanks in advance.
A "no-erase ipsw" is used when you want to go from a jailbroken device to iOS without losing data. In your case, you are already on iOS and seeing as how you have eliminated all of the potential software fixes, you most likely have a hardware issue.

Depending on the problem, the data may be recoverable but it would have to be looked at by a repair shop that specializes in iPhone data recovery.