Low Call Volume iPhone XR

I have an iPhone XR and for the last few months have been experiencing low volume on calls to the point that it’s almost unusable as a phone. It has had times of going back to normal (ie, the volume being higher) but more consistently of late it’s been very low. When I use speaker mode it’s fine, very loud, but obviously I can’t use this for all calls. Volume is also fine if I watch a video/ listen to music etc.

I don’t think it’s my screen protector as sometimes call volume has been fine with this on. For the same reason I don’t think it’s simply the fact the speaker needs cleaning.

I've tried switching it on and off silent, turning the volume up and down, turning it off and on again, turning airplane mode on and off, sliding the ringer volume thing up and down and obviously keeping up with updates but to no avail.

Apple are suggesting I take it in but I can’t easily get to a store and am dependent on having my phone. Just wondering if anyone had any thoughts or tips please? Thank you!