Accidentally Blocking Contacts?

My mother has an iPhone XR, all software current, do not disturb is off, airplane mode is off. All of her calls from contacts to call her regularly seem to keep going to blocked callers list. she’s very upset. Says she has no idea how this is happening, this is the second time in a week. She’s ended up with With my sisters and I blocked, several of her friends who call frequently are blocked.

Is there anything that she could be doing when a call comes in or when she hangs up that accidentally blocks these callers? Since she is elderly and has frequent falls, we need to be sure that our calls get through yet we have no idea how she keeps blocking us and neither does she. Thanks for any information you can provide.