Brian Swan has posted two more in his "SQL Server Driver for PHP" series looking at some of the connection options that are available. In these two new articles he looks at the Failover_Partner and Encrypt options.

Database mirroring is primarily a software solution for increasing database availability. [...] When a PHP application connects to the primary server, the Failover_Partner connection option specifies the name of the server to which the application should connect if the primary server is not available.

[...] These two options, Encrypt and TrustServerCertificate, are often used together. The Encrypt option is used to specify whether or not the connection to the server is encrypted (the default is false). The TrustServerCertificate option is used to indicate whether the certificate on the SQL Server instance should be trusted (the default is false).

In both there's code examples showing the connection strings and what kinds of parameters you can pass to them. He also gives a few examples of scenarios when they might be useful.