simply put; putting it simply
Used to introduce a simplified explanation or summary of a complex topic.
Simply put, the problem is that we don't have enough money.
Putting it simply, his opinion is against it.
Means 'in short' or 'the point is', often used to summarize after a longer explanation, while 単純に言えば is more about simplifying a concept.
Phrase composed of 単純 (simple) + に (adverbial particle) + 言えば (conditional form of 言う, 'to say'). Literally 'if said simply'.