Finally got in contact with Apple today. Tried to set up an express replacement under Applecare+ via chat but the tech is trying to push "tips on improving your battery life" on me instead.
I'm gonna send it in for service, but the diagnostic test he ran said things looks okay on his end.
In the end if it's the phone itself, I dunno what to do other than just sit on my hands and wait. There's no sense in "upgrading" my phone right now when we're about four months away from new devices. (Not to mention that none of Apple's current offerings interest me, but that's a separate issue entirely.)