"Why are you always looking at your phone?"
"为什么你总是在看手机" or "为什么你总是在看你的手机“ could be alternate translations of the same sentence. (They also sound more correct to me.)
I was wondering where the possesive 你的 went!
In Chinese, as in many other languages, constant use of possessive pronouns sounds like overkill! To say "Give me your hand!" an Italian would normally say "Give me the hand!" To say "Give me YOUR hand," would sound unnatural and like overkill. In short, in this sentence, it's not really needed but it won't be wrong if used.
因为我总是用手机学习汉语。 ;) (actually I would prefer 一直 yīzhí > yìzhí “all the time, continuously, perpetually” instead of 总是 but I guess you could use 总是 as a repeat of the question.)
Yes, but usually it duolingo only accepts it after a period of repeated reporting.