All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
Your statement, “I will give my phone as Waqf,” is a promise to make it a Waqf (endowment) and not a binding Waqf, so you are not required to do anything. Whoever holds a sincere intention to give in charity but does not have money to spend in charity therefrom, Allah, The Exalted, grants him the reward for that charity (for his sincere intention). It was narrated on the authority of Abu Kabshah Al-Anmaari that he heard the Prophet say: “The worldly life is only for four categories of people … (and he mentioned of them) … a slave whom Allah blesses with knowledge but not with wealth. So he holds a truthful intent, saying: ‘If I had wealth, I would perform the (good) deeds performed by so-and-so with it.’ He is rewarded for his intention, and therefore their rewards are the same…” [Ahmad and At-Tirmithi]
Thus, if you hold a truthful intention to make a Waqf and you do not have wealth to do so, it is hoped that Allah, The Exalted, would reward you for your intention by His Grace and Favor.
Allah Knows best.