The Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW) calls Tyfos a ring cairn, and suggests that the recumbent stones are simply kerb stones rather than an actual stone circle. There is no evidence that the stones ever stood upright, but it does seem that several have been removed. The circle lies within a larger circular area of levelled ground, so it seems likely there was much more to the site than just a stone circle.
The stones average between 1 and 2 feet tall. It is possible that the stones were erected first, and the cairn added later. Since you can see the Moel Ty Uchaf site (though not the stones themselves) from Tyfos, it begs the question of whether the two sites were related.
You can clearly see the stone circle from the road, but for a closer look you can ask at the farmhouse for permission to enter the field and wander amongst the stones.