Missing number, treated as zero within simple parbox/spacebox macro

I have a macro using parbox, spacebox, and some simpler whitespace. This generates a "Missing number, treated as zero." error for every time I use the macro. It still compiles to a PDF successfully with at least some distributions. (Overleaf succeeds; Windows MikTeX fails from something in the file but I’m not sure whether it’s this.) But what’s going on?

newcommand{PersonalEntry}[2]{
    noindenthangafter     % Indentation
    parbox{spacebox}{     % Box to align text
    textit{#1}}#2 par}    % Entry value
(...)
PersonalEntry{Phone}{555 555 5555}

Full error message:

! Missing number, treated as zero.
<to be read again> 
                   protect 
parbox ->protect 
                   parbox  
PersonalEntry ...-> noindent hangafter parbox 
                                                  {spacebox }{ textit {#1}...
l.128     PersonalEntry{Phone}{555 555 5555}
                                             
A number should have been here; I inserted `0'.
(If you can't figure out why I needed to see a number,
look up `weird error' in the index to The TeXbook.)