Leave room around the vocal
Use arrangement and level before making the vocal brighter.
Identify the crowded phrase
Choose a phrase where the words become hard to follow. Listen to the surrounding instruments rather than judging the vocal alone.
Temporarily lower a competing instrument to test whether the issue is masking. Restore the original level before deciding how to proceed.
Use the smallest useful move
Try a small level adjustment or section-specific automation on the competing part. Preserve its musical role when the singer pauses.
If tone processing is useful, compare with the earlier balance at similar loudness. Extra brightness can change consonants as well as intelligibility.
Follow the performance
Check quiet words, held notes and strong consonants across the song. A single setting may not suit every phrase.
Keep any phrase automation deliberate and review it with the full arrangement. The aim is a readable performance that still belongs in the song.