Whenphrase is applied to successful parse result which haslastFailure, it returns only the original failure.
I think it would be better to add a message that indicates the EOF is expected in the same way as it does when lastFailure isNone.

For example, the followingp fails because there are trailing spaces afterd, but error message comes fromc parse failure which doesn't have any hint for EOF.

val input = "a b d  "val p = phase(/* a parser that parses `a b (c or d)`*/)