Whispering is an unvoiced mode of phonation in which the vocal folds (vocal cords) are abducted so that they do not vibrate; air passes between the arytenoid cartilages to create audible turbulence during speech. Supralaryngeal articulation remains the same as in normal speech. In normal speech, the vocal folds alternate between states of voice and voicelessness.
Reciting Quran in Zuhr and Asr Prayers must be with Ekhfaat which means with low voice which can be heard by you in usual cases. It is like whispering with out clear voice. Just moving the lips with out hearing anything is not enough in Ekhfaat.