Even with the water resistance of the latest phones it's not impossible, more likely improbable. There's a seal in there to prevent that from happening, but maybe.
I wouldn't rule anything out. The sim tray on my 6s was sealed better than the 5s. The iphone 7 and above are at a minimum ip67 rated. So I agree with the poster above improbable is the word, but one never knows depending on the situation.
Lets start Which phone are you even referring to? Because there are phones in the past that don’t have a seal that surrounds the sim tray to help prevent water/dust to penetrate inside. Newer phones today, that would be more difficult to do, because they are rated for us as such with protective seals.