When the main speaker was absent, a colleague had to take his place.

take 是动词，意思是"拿、取、占据"。 his 是代词 he 的所有格形式，意思是"他的"。 place 是名词，意思是"位置、场所"。 take his place 是一个固定短语，字面意思是"占据他的位置"，引申为"代替某人"的意思。