Reid spent 15 minutes on the phone while routing 3 phone calls. In all, how many phone calls does Reid have to route to spend a total of 35 minutes on the phone? Solve using unit rates.
Reid spent 15 minutes on the phone routing 3 phone calls, so he spends 15 minutes / 3 phone calls = <<15/3=5>>5 minutes per phone call.
To spend a total of 35 minutes on the phone, Reid would need 35 minutes / 5 minutes per phone call = <<35/5=7>>7 phone calls. Answer: \boxed{7}.