We wrote in our journals for twenty minutes each day.
Answer:
adverbial phrase
In our journals cannot be a clause because it does not contain a subject and a verb.
It is a prepositional phrase because it contains a preposition, in, an object of the preposition, journals, and a word that modifies the object, our.
In our journals is prepositional phrase that acts as an adverb because it is modifying a verb, wrote. It is answering the question "Where?"
A prepositional phrase that acts as an adverb is an adverbial phrase.