My experience is completely different, Winchester. I know a lot of 8 year olds with their own phones. Some are restricted to incoming/outgoing calls/texts to specified numbers and are used to check in with parents when children walk from school or when they are out playing/at sports practice/sleeping over somewhere. Some are full-on, all-the-bells-and-whistles smartphones.
My own DCs had their own phones at 8. They used them at sleepovers and their friends had their own phones to use for sleepovers. My DCs are now aged 17 to 28 so it's been a long, long time since the first got her own phone and obv the earliest phones were very basic brick-type models with extremely limited functions.
My DCs also all (apart from DD1) had the experience of EOW visitation with their father. They used their phones to contact me while there, and I used their phones to contact them. It was agreed in mediation (required as part of the divorce process) that there could be unlimited contact - within reason - between both parents and all children.
The 'within reason' bit was sort of in the eye of the beholder, but it basically meant a few texts back and forth or one or two phone calls a day and a call to say goodnight was perfectly reasonable, and importantly this was permitted for both myself and my exH. Hence the phones, and if a parent used a home phone/landline to call, it would always be picked up or the call immediately returned, because it was recognised - or it was supposed to be recognised - that the children had the right to contact the other parent and the other parent had the right to contact the children even during the other parent's parenting time.
I say 'it was supposed to be recognised' because exH always saw contact between me and the DCs during his weekends as a slap in the face to him and he found ways to punish the DCs for contacting me.
This is why I am curious about whether the father ever calls the child when she is at the mother's house, why I am asking if he has that right, and whether he exercises it, or if he is content to go through a middleman who might or might not pick up a phone to facilitate a conversation and thus a relationship.
Although my exH took umbrage at contact between me and the DCs during his parenting time he rarely if ever got in contact with the DCs during the twelve days when they were with me, and the DCs interpreted the EOW visitation as lip service to the idea of a relationship on his part at best, and at worst - when the punishment for contacting me was taken into account - as a game of keepaway on his part; they felt he was only interested in the visitation because it meant he was being accorded his legal rights and keeping them away from me for two days out of every fourteen.
I am interested to know if the father is in regular contact with his daughter when she is with her mother and if so how this is arranged.