Microsoft SQL Server runs on a virtual machine. This VM can be switched to another physical host anytime, however the SQL Server installation remains on the same VM. Do we need Software Assurance (license mobility) for the respective VM or not, since we do not license the physical host but the VM?

Even if you license Microsoft SQL Server per single virtual OSE, the software may only be run on a fully licensed server (physical host). If the VM can be exchanged between the physical hosts, licenses need be reassigned accordingly. Without Software Assurance, this can only be done every 90 days. If the VM should be reassigned on an as-needed basis, Software Assurance is required.

Source: Microsoft Product Terms, November 2018