I used VOIP app Acrobits Groundwire on ios for years until very recently, when I did not want to be tracked by the cell provider. I used it on open wifi connections (via a personal VPN) to make calls. It has a lot of features, including automatic recording (optionally, with each party on their own channel) which I used and really liked. I am shortly going to be determining how/if it will run on GrapheneOS as it is available for Android. My guess is "not totally" as it very likely relies on Google's push service, however it may still work with polling and for outgoing calls. (I do not intend to install Play services at this time.)
However it is a VOIP softphone app, so you will need to subscribe to a VOIP service and number to use it and cell data service on your phone. That is not a big cost whatsoever.
VOIP providers like voip.ms can be configured to automatically record (and transcribe) calls, which eliminates the need for on-device recording. In my case, I have used provider recording AND the Groundwire VOIP softphone to record important calls because I could not afford to not have that recording, and this gave me a backup in case one recording failed (which never hapenned).
You could forward your current cell phone number to the VOIP service and then have it forward back to your phone as a VOIP call, to record it.
also, voip.ms lets you make outgoing calls through it where your number is masked and your VOIP number is used instead. I really like the ability to not disclose my cell number, and to be able to use a easily replaced VOIP number instead, because we all know that your number will end up in someone's phone where Facebook, Google, etc. will grab it.