So nothing to do with settings or so.
Did you tried to connect just the phone to the Spark without the RC? You will be limited to 100 meters distance and 50 meters height. But if that work fine, the issue is probably with the RC.
Best is to be in an open area with minimum wifi around you. Depending on your countries and type of phone type (older android phone could have issue to detect 5.8G wifi channels) the best is to try at 2.4G by powering the Spark, wait it blink yellow and then press the
battery button about 10 seconds until you get 3 consecutive beeps. There will be 1 beep, 2 beeps and then 3 beeps. The wifi will be reseted to 2.4G with default SSID. You should be able to connect to it as SSID Spark-xxxx.