Having had the privilege of studying existential phenomenology under Edward Gannon, S.J., I think I can fairly say that while it is necessary to read Sartre, it is equally necessary not to take his existentialism as definitive. Being and Nothingness, which is really just Sartre's version of Heidegger's Sein und Zeit, has to be one of the most boring books I have ever read (in that sense, for sure, it accurately reflects Heidegger). But there is more to be got in the sense of a practical philosophy from the writings of Gabriel Marcel and Albert Camus. Jacques Maritain's Existence and the Existent and Martin Buber's I and Thou are very important as well.
The important thing about phenomenology is that by forcing one to focus on observing things as accurately and precisely as one can, it protects one against emotional exhibitionism. So many people these days seem to think that by expressing their feelings in some vehement manner they demonstrate the soundness of their thinking. What they demonstrate is intellectual laziness and emotional incontinence One has to examine things carefully in order to determine if one's thoughts about them are sound. More often than not, one discovers that things are a lot more pedestrian than one's feelings about them.
Sartre may have posited that a person is an object for all other subjects ("Hell is other people"), but Marcel and Camus and the others did not. The very point of existentialism is to see the other as a person. Otherwise you reduce your engagement with that person — and yourself as well — to mere functions. Getting on the bus, handing the driver your fare, taking your transfer and then sitting down is an example of that. The insertion of three words, "please" and "thank you" changes that into a personal encounter.