Moving Lips
The mode of recitation in all salat, as commanded by God Almighty is to use a middle voice, which is neither too quiet nor too loud. Please see verse 17:110 for clear instructions on how to recite salat: 17:110 Say: “Call on God or call on the Almighty; by whichever you call on, to Him are the best names.” And do not be too loud in making your contact prayer, nor too quiet; but seek a path in between. Hence, reciting salat in heart or just by moving lips alone is not recommended and appropriate, according to Quran. It should be recited in a way that your own ears can hear it.