The Pentagon is already determined to make a stand at Guam in case of war:
To put it simply, the US military is going "squeeze all kinds of SAM systems possible onto every inch of the island." Guam is expected to be able to take a very hard beating from Chinese aerial, naval and rocket attacks following those upgrades. Then, there's also the US Navy warships that can provide SAM cover for Guam with their SM-3s and SM-6s as well.
Plus, even if once Guam is finally knocked out and rendered completely ineffective for the US war effort, the US military has planned to fall back to Wake and/or Micronesia, both of which are even further away from China than Guam is, i.e. the 2.5IC (~1000-2000 kilometers east of Guam). Hence, China must also be able to reach those places along the 2.5IC too.
Tl; dr: To knock the US out of the war in the WestPac, it will never be easy, and it will never be limited to Guam only.
China and the PLA still has a lot, and I mean
A LOT, to do.