Mouth the lyrics

• Just pretend to sing
• Fake it, musically
• Not really sing
• Mouth the words to a recorded song: Hyph
• Go through the motions in a music video?
• Mouth some music
• Sing along silently
• "Sing" without singing
• Align mouth move­ments with recorded speech

Wiktionary Word definitions in Wiktionary
n. (alternative spelling of lip sync English) vb. (alternative spelling of lip-sync English)