Answer:
The absolute phrase in the sentence is the NP "their boots sticking with every step".
Step-by-step explanation:
The NP "their boots sticking with every step" is an absolute phrase. An absolute phrase is a phrase that modifies a sentence but it is not connected to the sentence by a conjunction. It is set off with a comma and can be removed without altering the meaning of the sentence (see 1). Typically, absolut phrases consist of a noun and a modifier.
1) The company trudged across the muddy fields