The picture says this is Psalm 18. If you find the specific translations, yes the phrase “the Lord is my Rock” comes from Psalm 18:2. It should be noted that not all translations use the word “rock”. Why might this be? Maybe because the image of a rock does not necessarily convey the entire meaning of the original language. The root of the meaning is “lofty”; a craggy rock, literally or figuratively (a fortress)
If you talk about a “rock” to the average American, their mind likely thinks of a stone they can hold in their hand. Those of the a certain age will even remember “Pet Rocks”. This type of rock is usually small enough to hold in your hand, is relatively smooth in texture and is easily thrown away by even the smallest child. When the early Hebrew heard this passage (most never read it personally), they imagined a large (lofty) immovable stone structure that could be held on (craggy) to during a storm, or the stone could provide protection from attack (a fortress).
So I ask, what is God to you? Is he your “Pet Rock” that you take out when you want to see it and toss it aside when you have no use for it that day? Or is He so large in your life that everyone who sees you, sees your Rock and knows you cannot be moved from Him?