There are 13.
This DnDBeyond search shows several on the Warlock spell list:
- Create bonfire (cantrip)
- Green-flame blade (cantrip)
- Hellish rebuke (1st level)
- Spirit shroud (3rd level)
- Elemental bane (4th level)
- Sickening radiance (4th level)
- Wall of light (5th level)
- Investiture of flame (6th level)
- Crown of stars (7th level)
And on the Celestial Warlock's expanded list:
- Sacred flame (cantrip)
- Guiding bolt (1st level)
- Flaming sphere (2nd level)
- Wall of fire (4th level)
- Flame strike (5th level)