Telephone in Care Home

Could I suggest you start by asking members of staff what they do when they need to use their phones. We had exactly this problem when my dad moved into a care home but on staff recommendation we switched his phone from EE to Virgin and the signal was fine

Thank you both that's interesting. Mum has a basic Alexa but we haven't been able to connect it since she moved in (it worked fine at her other care home). This is something I thing we need to speak to the care home about, as in her room is some sort of hub but no router. I do think the Alexa or Google assistant could work though!

There are a few ways of using a VOIP (Voice Over Internet Protocol) phone with your mum but your mum would need to sign up to a VOIP service provider. Your mum would have a phone similar to a regular landline, connected either wirelessly or wired to the router in her room. I don't know the cost of these.

However, have you thought about using one of the 'Assistant' technologies such as Alexa, Siri or Google? Once set up, your mum would only have to tell the Assistant to phone someone and can also receive calls which can be also screened.

This will require the use of a smart phone (which she already has) but not require her to make calls or answer it in a conventional sense. However, the mobile would need to be kept charged and some occasional input.

My DF has an Amazon Echo show. This links to the Alexa app on the mobiles of family members. Once set up all he needs to do is say, "Alexa call Pittcity" and "Alexa hang up".
My DS linked it to his contacts in his mobile phone.
You can have voice calls or video calls.