The phone port of these surge protector is for phone, fax machine or cordless phone only. Not for the modem.
These surge protector's phone ports are not only protect from surge but also filter the noise from phoneline. It will absorb the dsl signal from the phone line too.
Instead, the adsl/vdsl modem will have the built in surge protect inside; but then , the quality and strength of the modem's surge function is variety by the model and brand.