You don't need to use tabs anymore in PhpWiki. Consider this page obsolete. See TextFormattingRules for how to use PhpWiki markup.
VariousBrowsers have trouble with the tab character used in the TextFormattingRules. If you can't type a tab, or, if you are fixing up a page written by someone who didn't type tabs, then you should have us convert spans of spaces to tabs for you. You request space to tab conversion with the checkbox that appears near the bottom of EditText and EditCopy pages. It looks something like this…
[[[[o]] I can't type tabs. Please ConvertSpacesToTabs for me when I save.
A span of spaces must be at least three spaces long to be recognized as a tab. Use multiples of eight spaces to make multiple tabs. Each span of eight spaces will convert to one tab. If the last span comes up a little short, that's ok, as long as there are at least three spaces in the last (only) span.