Air carrier First Officer reported missing the last part of an ATC clearance due to chatter on guard frequency which the flight crew was monitoring. The reporter stated the chatter seems to be increasing and causes confusion at critical phases of flight.

Narrative

Our filed cruise altitude was FL370. At the time of the event; we were climbing through FL300 for our last cleared altitude of FL310 near the ODI VOR. ATC called us and said 'Aircraft X; climb and maintain FL........' I could not hear the last part of the transmission over someone saying '[political utterance]' on the guard frequency; which the PM and I were both monitoring on the 2nd comm radio. The PM thought he heard FL350 and I wasn't sure what I heard; although I had already started spinning up the altitude pre-select knob. For a minute while we tried to request clarification on a busy center frequency; there was confusion between myself and the PM on whether to continue climbing or leveling at FL310; which was quickly approaching. The PM eventually clarified the clearance to FL350 and we continued to climb with no incident. We were unable to fully hear a clearance from ATC because of inappropriate use of the guard frequency. This 'trend' seems to be increasing recently so it's no surprise it eventually led to us missing a clearance and causing unnecessary confusion in a critical phase of flight (less than 1;000 ft. to level-off). I'm submitting this as a data point of inappropriate use of the guard frequency.