To speak on someone's behalf/ speak in the name of/ to be spokesman (mouthpiece)
Spoke in his place. Served as his spokesman. Argued his points on his behalf.
("And he shall speak to you to the people, and he shall be to you a mouth, and you shall be to him a God" - Exodus 4:16 (God to Moses), and so: "Among all the inhabitants of Be'at/ Who has not been to you a mouth" - Nathan Alterman/ Poems on the Land of the Negev)
Translation
Expression (Hebrew)
הָיָה לוֹ לְפֶה
Definition (Hebrew)
דִּבֵּר בִּמְקוֹמוֹ. שִׁמֵּשׁ כְּדוֹבֵר שֶׁלּוֹ. טָעַן טְעָנוֹת בִּמְקוֹמוֹ.
("וְדִבֶּר הוּא לְךָ אֶל הָעָם וְהָיָה הוּא יִהְיֶה לְּךָ לְפֶה וְאַתָּה תִּהְיֶה לּוֹ לֵאלֹהִים"- שְׁמוֹת ד טז (ה' לְמֹשֶׁה), וְכֵן:"בֵּין כָּל מוֹשְׁכֵי בְּעֵט/ מִי לֹא הָיָה לְפֹה לָךְ"- נָתָן אַלְתֶּרְמָן/ שִׁירִים עַל אֶרֶץ הַנֶּגֶב)