A verbal is the form of a verb that is used as a different part of speech.
In English there are three verbals--participles, gerunds, and infinitives.
Participles can either be past participles or present participles and they act as an adjective.
Gerunds always act as a noun.
Infinitives in a sentence may act as a noun, an adjective, or an adverb.
A verbal phrase is a phrase consisting of a verbal plus any complements or the verbal plus any modifiers to the verbal or the complement.
For more see the glossary entry on each individual verbal type.