phonehelp what compromises to my privacy am I giving up here?
It depends what your threat model is and what you consider a compromise to your privacy. If don't want that secondary profile linked to your real identity, then you might want to consider creating and using a dummy google account.
phonehelp but am I giving up things like my phone number to both google and app maker if I do so?
I'd suggest giving the FAQ a read through to better understand hardware identifiers and non-hardware identifiers, specifically: https://grapheneos.org/faq#hardware-identifiers
To my knowledge, only apps with the phone permission are allowed to access the phone number, which can only be granted with the user's consent in the form of a permission dialogue upon opening said app.
Here's more specifics on how Sandboxed Google Play Services works: https://grapheneos.org/usage#sandboxed-google-play