In the provided sentences, the following underlined phrases are prepositional phrases:
- off the road (from "I drove my car off the road to fix the flat tire.")
- in the basement (from "We took cover in the basement during the thunderstorm.")
- under the surface (from "We strapped on our goggles so we could see the fish under the surface.")
The phrases "to be" and "to fix" are infinitive phrases, not prepositional phrases.