I believe it was Sagan that speculated it was tidal forces that caused the fractures. Then water, heated by tidal friction, escaped from the fractures, creating the small crater chains that are part of some groves.

But what if those groves, where we see such crater chains, were really water rich layers of a larger world. And this water escaped because of tidal heating and the escaping water caused the crater chains(simular to what Sagan proposed). This might explain why some groves have such crater chains while other don’t.

The groves are probably tidal related, but it would be interesting if they were actually layering put down when Phobos was part of a bigger, younger world.