You are mixing things up.
Maximum altitude tello can fly is 30m above takeoff point. That is an internal lkmit that cannot be modified. And it requires a stable wifi connection.
Wifi connection quality and range depends on a number of factors. Your phone is a factor just as Wifi and other rf interference.
And very important is position. Never fly directly above your head. If you want 30m altitude you should fly at least 30m horizontal distance away.
If you dont believe me read up on radio distribution patterns of vertical polarized antennas
I often go to 30m alt without issues, and 70m horizontal range with good quality. Max range without repeater was 120m, but with bad video feed