Diagonal screen size is a terrible measurement when different phones have different aspect ratios.
That said, even when going by volume, this isn't a particularly small phone at 94 cm3.
A current-gen iPhone SE is only 68 cm3. The zenphone 10 sits in between the 81.8 cm3 iPhone 14 and the 99 cm3 iPhone 14 Pro Max.
Or compared to Samsung, the "regular sized" Galaxy S23 is 78.8 cm3. Even the S23+ is slightly smaller at 91 cm3! Only the S23 Ultra is significantly larger at 114 cm3.
(All volumes here were determined by multiplying the deminsions listed on GSM Arena. They're probably all slightly off due to camera bumps, but should be comparable to each other.)