The Mishna Berura advises length and direction for foot motions before and after Shmoneh Esrei. Many, possibly the majority, of small Ashenazic (and Sephardi) shuls are so packed with seats that it is not possible to comply with the Mishna Berura in there. Of course the individual davener is not obligated in what he can’t do. But aren’t the people who create shuls obligated to make it possible to comply?
From my understanding of the Mishna Berurah (123- 13,14) that a “step” here is like the steps the kohanim did in the Bais Hamikdash, which was merely moving one’s heel until the toes of the other foot. Therefore the way the steps should be done (for a right-handed person) is as follows. Move the left foot back until the toes are in back of the heel of the right foot, then move the right foot back until it’s toes are in back of the heal of the left foot. Then move the left so it will be parallel to the right foot. If you measure it, the person’s body, (not the front of the foot) will have moved back about 60 cm, or 2 ft. I think it is something the individual can definitely do. If you are short on room you can also take the steps back at an angle. Personally I rarely have a problem. Rarely I might have to take the last step in a way that my foot goes slightly under the bench behind me for a minute. In the rare event that even that is not possible, he may take shorter steps.
Taking the three step back is important. The gemora in Yoma 53b says that one who doesn’t take the three steps back is better not to daven! Even someone that has to daven on an animal should move the animal back the three steps! (Rema O:CH 94-5), and the same with a person in a wheel chair, (Halichos Shlomo 8-30).
The idea of the 3 steps is that when we daven Shemona Esrei we are actually standing in front of H-shem and we take the 3 steps to depart and “come back down” to this world. If we don’t take the steps we are showing that we didn’t understand where we really were and what we were doing.
Aruch Hashuchan 123-5, Also see Eishei Yisroel 23-58, where he spells it out clearly.