If you come across this word "말하자면" in a text, you should detemine whether it to be an adverbial or just plain condition phrase. Like Engllish, the adverbials are usually placed at the beginning of the clauses in Korean.
The adverbial "말하-자면" is a contraction of the phrase "말로 하자면", meaning "so to speak" in English.
무엇을 말로 (표현)하다(or 설명하다)
to express something (for examples a state, situation, event, etc) in words.
to give details about something in words.
In the phrase "말로 하-자면", the connective ending "-자면" is used.
(이것을) 말로 (표현)하-자면, (with the connective ending "-자면")
And this phrase can be replaced with the following phrase.
(이것을) 말로 (표현)하-고자 하면/한다면, (with the connectvie ending "-고자")
Thus, sometimes, the adverbial "말하자면" can be replaced with the phrase "다시 말하면/말해서(to say/express in other words)"