Is it allowed to hold the Qur'an or a phone in your hands when performing salah due to not knowing the verses of the Qur'an by heart?
Bismihi ta'ala
There is no problem in doing so, although some jurists have mentioned that it is makruh to read off of something while praying, however it would be better to read off of the Quran, or dua book, or mobile for the purpose of performing that particular prayer, until one is able to memorise it.
And Allah knows best.