。
Could I speak to Mr. Brown, please?
Literal
Brown-honorific [object-を] honorific-request-do [polite-します].
A standard phone-call opener. お願いします literally 'I humbly request,' here used to mean 'please [give me / connect me to] X.' The pattern [person/thing]+をお願いします is the polite request for a specific item or person. ブラウンさん uses さん, the respectful neutral suffix for any name (English equivalent: Mr./Ms./Mx).