Is it permissible to write the Mushaf in phone applications using a script other than the Uthmani script, such as writing "مالك" (Maalik) instead of "ملك" (Malik) in Al-Fatihah? And is it then considered a Mushaf?

The orthography of the Qur'an is a followed Sunnah, and it must be written according to how the Companions wrote it. This is the view of the majority of scholars. Therefore, it is obligatory to preserve the writing of the Qur'an in the Uthmani script, especially if it is a complete Mushaf. An exception to this is writing an ayah or ayahs for a specific purpose, such as quoting or teaching, in which case it is permissible to write them in conventional spelling. If some words in the Mushaf are written in a way that deviates from the Uthmani script, this does not invalidate the Mushaf, even though it is fundamentally impermissible to do so.