Can two different definitions of acidity and basicity be used together?

I wanted to predict the pH of $\ce{PH3}$, it has basic nature as it has a lone pair of electrons. But it also has acidic nature as its $\ce{P-H}$ bonds are weak. Now according to the Lewis definition $\ce{PH3}$ is a base and according to Bronsted-Lowry definition it is a acid. Can we say from this that $\ce{PH3}$ is neutral?




Put simple: these are two *mutually independent* definitions.


* The Bronsted concept is based on the possibility to donate a proton (i.e., an acid), or to accept a proton (i.e., a base). But it isn't only the presence/absence of a proton in a compound, it equally depends on the reaction partner if a molecule may act as an acid, or as a base.
* The Lewis concept is based on the presence of an non-bonded electron pair (Lewis base), or empty molecule orbital (Lewis acid).


Since the two concepts take a different perspective, which is independent of each other, it is possible (but not a requirement) that the two concepts independently assign a compound to be an acid, or a base. It happens e.g., the hydroxide $\ce{OH-}$ anion indeed simultaneously is both a Bronsted base as well as a Lewis base. But since the two concepts are set up independently of each other, you can't «neutralize» acidity assigned by one theory with basicity assigned by the other theory.


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