Phone Calls Messing Up

I've been having a few issues with the call functionality on my iPhone. Two examples: a two factor authentication service that my school uses has the ability to call a designated phone number, and by pressing a key, the service allows access to an account. I have been running into an issue multiple times where the service will call my phone and my phone will not ring, but the online status update states that my phone in fact received and answered the call and is awaiting the key input. For clarification, I am certain the correct phone number is being used, and the same service has been working for other devices, just often times not on mine which makes me think it is likely my phone, not the service.

Additionally, my phone occasionally requires multiple attempts to call a contact before the call actually goes through, no matter the signal strength (the process typically goes like: press to call the contact, the phone quickly says it's calling the contact, the call will automatically fail, and this gets repeated a few times until the call goes through).

I have been having other call issues (calls dropping without explanation, weird call audio delays and warped sounds, etc.), but my phone has otherwise been working as expected (battery life, cellular data usage, processing speed, text and iMessage, "non phone call" app performance, etc.) I haven't had any physical damage to my device (drops, spills, overheat notifications etc.) recently either.

Does anyone know what potentially could be going on, and is there an easy way to fix the phone call issues?