Include "businesePhones" in basic profile
According to https://docs.microsoft.com/en-us/graph/permissions-reference#remarks-23, now with permission:"User.readBasic.All" , only bleow properties would be visible:
Which means "businessPhones" is not included.
So it means normal user (not admin) won't be able to view other users' business phones
Just suggest to include businessPhones in basic profile.