Why is there a doublet instead of a singlet in this Wittig reaction salt configuration NMR? I did an NMR sample to my salt p-carboxybenzyl triphenylphosphonium bromide. I got a doublet at 5.26, and according to every article it belongs to the $CH_2$ next to $P^+$, but how come I didn't get a singlet for that?
Phosphorous exists entirely as $\ce{^31P}$, and $\ce{^31P}$ has a magnetic moment of 1/2 (just like a proton). Therefore, a single phosphorous will split any protons coupled to it into a doublet - as you observed. If you looked at the corresponding $\ce{^31P}$ NMR spectrum you would see that the phosphorous signal would be split into a triplet by the two protons.