Can iPhones get hacked?

Hello I was under the impression that iPhones couldn’t get hacked but my mom was telling me that she keeps hearing conversations while she talks on the phone for a while. She’s been telling me this for a bit now it first started when she said she would be sleeping and her phone would just start going off in a full conversation with someone and she also says that sometimes she gets the “this call is because recording” while on the phone this leads me to this her phone is getting hacked