On Azure Custom Speech Service's Privacy Page you can request and collect all the privacy and GDPR related information that Azure Custom Speech Service is providing.
The privacy policy by is a legal document or statement that discloses how Azure Custom Speech Service gathers, uses, discloses, and manges their customers' data.
The basis for Microsoft sharing, adding, uploading, hosting, accessing or sending personal data out of Europe. Vendors can also add a description of their own impact assessment for data transfers.