Bonjour Shelley,

"Avoir envie de" is a locution verbale ( a group of words functioning as a verb)

There is a noun feminine "envie" meaning envy or jealousy.

There is the transitive verb "envier"  to desire / to envy

The locution verbal acts as an expression in its own right and so it doesn't make sense to try to analyse it word for word and should be accepted as it stands.

There is further information here, https://www.wordreference.com/fren/envie

Hope this helps.

Bonne continuation.

Jim