What exactly are the practical halachos of teffillin and flatulence? If one has any suspision that he may need to flatulate, he must abstain from wearing them? How should he proceed?
There is no need to abstain from wearing tefillin because of a suspicion that one might need to flatulate. However, while wearing tefillin, one must avoid actual the passing of flatulance, and stop oneself from doing so. If one feels that one cannot stop oneself (this is unusual), the tefillin (at least the head tefillin; see Magen Avraham 38:2) should be quickly removed. If one removes one’s tefillin in order to pass flatulence, one should recite a new blessing upon putting them back on (Mishnah Berurah 25:47).
Only somebody who has a stomach ailment, and who will constantly need to use the bathroom, should refrain from wearing tefillin until his stomach is in order.