Grammar is mostly independent from writing systems. It usually is a phonetic representation of the language. Usually a single symbol has a certain translation into a vowel or consonant, sometimes it is a group with such a translation (e.g. th, sh, ou, etc.)

With English, this is a bit different, because the great vowel shift and some imported typesetters created a discrepancy between the spoken word and it’s pronunciation on the one side, and that word’s written representation.