My son set up the Apple ID on the phone but now he has no clue what it was

hello, I wanted to put a sim card in an old iphone 5 that my son used to use to use on vacation. He set up the apple ID etc (hes now 19), he has no clue what it was. we charged it and had no idea what the passcode was so erased it, but it wants the apple id and password. since this phone he has had several and created a new account as he got older so this does not show up in his "find my iphone" or current account. Do I have a way to use this phone?

[Re-Titled by Moderator]