My impression (based on nothing more than anecdotal industry experience) is that there are far more jobs for PHP globally, and that the average starting salary for a new PHP dev is going to be considerably lower than the average starting salary for a new Go dev.
However, the number of stable senior PHP dev jobs with high salaries is also likely far higher than for Go.
I imagine it's easier to earn more as a new Go developer if you can get a job doing it, but it's easier to steadily get raises as a PHP developer.
I don't speak for the parent (and I don't think the assertion is correct), but I will say that PHP jobs outside the valley are plentiful. A large percentage of those are legacy maintenance or development on unpleasant platforms such as WordPress or Magento, but there is still a lot of challenging and enjoyable work being done using PHP, and the improvements to the language over the last few years have made many of the old arguments against the language obsolete.
That might not be a good measure, take a language related to PHP like Hack. The min salary for this language will be six figures because the only company that uses it is Facebook. PHP is a widely used language that your not going to have problem finding a job with.
StackOverflow's developer survey[0] would suggest that the original comment was incorrect. But I think it's an incomplete story for the reasons I and other respondents mentioned. The large supply at the lower end of the market depresses salary, but as one rises, salaries are in my experience comparable to any other widely-used language.
