You have a Teams Phone deployment. You have a site named Site1 that contains a Session Border Controller (SBC) named SBC2. SBC2 uses Direct Routing and does NOT have local internet connectivity. Site1

Location-Based Routing (LBR) is designed to restrict toll bypass and ensure that calls are routed and media flows through an approved SBC when local internet connectivity is not available or specific network topology dictates call routing. In this scenario, LBR ensures that SBC2 (at Site1) uses SBC1 (in the datacenter) for media and signaling due to the lack of local internet and the presence of the MPLS link.

While an SBC can technically proxy SIP messages, "proxy SBC" is not the specific Teams Phone feature designed to handle media routing and regulatory requirements for sites without local internet connectivity in an LBR context.

SIP options are used for SBC health monitoring and availability, not for dictating media path or call routing based on network location and internet connectivity.

Media bypass is for optimizing media flow by sending it directly between the client and SBC, bypassing Microsoft 365. This scenario describes a requirement to not bypass a central SBC (SBC1) due to lack of local internet, making media bypass an inappropriate solution.