SD Switch Port with Variable TTL

#1

Situation is as follows: (all switches are PepLink)
a) PC connected directly to switch sending “monitoring” pings to same IP segment through couple of switches receives steady response both for time response and TTL.

b) Same PC now connected behind Yealink T19 phone on the same port sending same “monitoring” pings, receives variable response on the TTL value while time response is steady.

Any idea on why TTL varies? Point in consideration is that Phone port is 100 Mbps while switch port is configured to 1 Gbps. Even moving down port speed reduces TTL variability but still it is not constant.

Any help is welcome

Saludos