Have a look here - the first one should fit the bill - has bluetooth for connection to car + all basic functions - is Amazon's UK first choice and less that £30 and of course the Amazon returns policy if you Dad can't get on with it.
https://www.choose.co.uk/guide/best-...r-elderly.html
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Denver GSP-110 Big Button Mobile Phone For Elderly - Unlocked Senior Mobile Phone, SOS Mobile Phone, Senior Mobile Phone with Talking Numbers, Bluetooth, and Torch
All the best
Martyn