Gamabunta summoned to fight against Shukaku. During the attack on Konoha, Naruto summoned Gamabunta to save himself from being crushed by Gaara's Sand Waterfall Funeral. Gaara was in his full Shukaku form, although Gaara's personality was still dominant at the time.

Can Naruto still summon Gamabunta?

He probably didn't have confidence he could use it again. This is evidenced by the fact that in his fight with Gaara later, he only successfully summoned Gamabunta again because he was about to die, failing the first time by summoning Gamakichi.

Who can summon Gamabunta?

Later, after the young man began training with the toads, Bunta was the one to tell him that the Great Toad Sage was looking for him in order to bestow a prophecy upon him. Gamabunta was later summoned by Jiraiya, alongside Manda and Katsuyu during the Second Shinobi World War.