Look at it from the other persons perspective they 1) feel comfortable doing this and 2) have the financial means to do so why not let them give their best friend a nice guilt? I’m very fortunate to be at the income level I am but as a mom of a 19 and 20 year old if they had asked me to give their best friend a phone I would ask some questions like, do they need one? How old is theirs? Why can’t they afford one? Assuming they had a shitty old phone because they’re poor I would absolutely be ok with my kid giving a (long term) best friend a phone, especially if the friend was also open to it

Assuming they’re just well off and have normal parents I think it’s very possible this is a reasonable gift.

Anytime we have an expensive gift to a friend they personally called us on the phone to thank us, it was always awkward as hell to me but polite, so I think that’s the etiquette when you get a gift life this, to call and say tanks in person or to see them and thank them in person (the kids parents, assuming they bestie didn’t pay for it all on his own in which case that’s between the two of them imo)