A verbal phrase is a verb acting as a noun or adjective and not as a verb.
Here is a sentence from chapter 17 with some verbals in it.
So unchanging was the dull old house, the yellow light in the darkened room, the faded spectre in the chair by the dressing-table glass, that I felt as if the stopping of the clocks had stopped Time in that mysterious place… (ch 17, p. 88)
If you take the first clause and re-arrange the words, it is easier to see what each one is.
The dull old house was so unchanging.
This is a participial phrase. In this case, it is clear that “was” is the verb and “unchanging” is a predicate adjective. In other words, “unchanging” is an adjective from the verb “change” used to describe the house.
A second example is the word “dressing-table.” In this case, it is a gerund phrase. A gerund is a noun made from a verb. The verb “to dress” has become the noun “dressing.” A “dressing-table” is a table where you dress.
Finally, we have “stopping.” Again, you can tell that this is a noun because it says “the stopping.” It is actually also a gerund, and it is the subject of the sentence.
This same chaper contains an infinitive earlier on.
The interview lasted but a few minutes, and she gave me a guinea when I was going, and told me to come again on my next birthday. (ch 17, p. 88)
The infinitive phrase is "to come again on my next birthday" based on the infinitive "to come." An infinitive is a verb preceded by "to" and is an unconjugated verb.