Aside from the fact that PHP, while I personally would never use it, can and has been used to write scalable software, computing is more than just a few poor coders.
It's a bit like saying that being a doctor can't be considered a profession because there are homeopaths. Your argument is neither convincing or logical.
And it's not like saying that doctors aren't a profession because there are homeopaths, because homeopaths aren't doctors. The segment of our industry that is more EE than CS is highly professional, somewhat organized, and relatively mature for an industry only fifty years old, but they are a small, nonvocal segment of our industry and they tend to distance themselves from the people who call themselves "developers."
Let's put it another way - just because some people dig ditches doesn't stop construction from being a profession.
The fact is that Computer Science is a profession. You might not like certain things about it, but you are deadset wrong if you don't consider it a profession.
The litmus test is whether or not an occupation has a policing organisation who dictates who is allowed to practice it. Lawyers, doctors, civil engineers are professions. Homeopathers, developers and ditch diggers are not.
I'll reference wikipedia, but its more of an unwritten rule.
Here's 1 easy to find example, note the advertised rate on odesk https://www.sugarsync.com/piv/D8109283_67296521_859910
People writing PHP for $15 an hour in India are seen as the same level as people writing PHP (or other language) for $125 an hour in the US and Europe.