I have no RC (Controller). In this scenario, I can reach 50m high (software limited to that high)

  

  

What is the best way to guarantee connection between phone and spark on that altitude? (to make a picture)

  

  

Phone right below Spark (50m straight line), or a bit away front it? For example, 30m to the left and 50m below (58 meters – right triangle formula/Pitagoras)

Well I suppose it depends which way the antennae  are orientated, but yoy can't see them.
(BTW, when I use no remote, I use crystalsky, and the height then is capped at 30 metres.)

Yes, the position of antenna is important. You can take the attachment as reference. In addition, open airplane mode can reduce reference.