If it is a prepositional phrase, determine whether it is used as an adjective or as an adverb.
"Practical Grammar and Composition"
Thomas Wood
Parenthetically, all Akor-Neb family-names are prepositional; family-names were originally place names.
"Last Enemy"
Henry Beam Piper
2. The prepositional form.
"The English Language"
Robert Gordon Latham