What a mission today has been. I think I’ll ultimately roll back to using Debian Jessie as Stretch isn’t a supported system, yet.
To get the MS SQL ODBC driver working even in Jessie appears to be a challenge. In Stretch I almost surrendered. It is working, but I do think it’s a bit of a hack as I’ve had to install an older
libssl1.0.0 and enable the locale
PHP development voted out the inclusion of MS SQL to the project so now you must compile and install it yourself. There are some very good instructions out there to help you – even from Microsoft.