Device data in general can only be retrieved if the device has one or more of the following protocols enabled: FTP, HTTP, HTTPS, JetDirect, MOB (Managed Object Browser), SIP, SMTP, SNMP (SNMPv1, SNMPv2 or SNMPv3), SSH, Telnet, WMI. More detailed network device scanning requirements can be found in
this knowledge base article.
The MAC address specifically can only be retrieved if the device has SNMP or (in the case of Linux and Mac) SSH enabled, or if the Lansweeper server is in the same subnet as the device. If enabling SNMP on the phones is not possible, you would have to add your Lansweeper server to the phones' subnet or add an additional scanning server in order to detect the MAC addresses. (You appear to own a Lansweeper Premium license, which only allows for one scanning server.) If you already have a list of your phones and their MACs somewhere, you could import it into your installation by following
these instructions.