I'm a beginner myself but I'll chime in
For a website of this type, the contact information is of high importance. Therefore, relying on an image as the sole contact information is not a good idea.
I don't know how php works, but I would imagine it also supports the "alt" attribute. Alt is the alternate
information that will be displayed if for any reason the image is not fetched when the browser loads the web page. So I would suggest keeping the image there, but in the php code (if supported; again I'm unfamiliar with it), add the alt attribute as shown in the code below as a "plan b" of sorts, in case the image doesn't load.
Also, some people may be too visually impaired too see web pages, and rely on the text of a web page being spoken to them via accessibility software. Accessibility software does not know how to read the numbers on an image...all it can understand is that there's an image.
Lastly, some people still use dial-up which is insanely slow, and they may turn off image rendering in their browser so they can load pages faster. Again, this would prevent them from seeing the contact info if it is only conveyed via an image
Anyhoo, here's how it would look in HTML; hopefully it works the same in php (worth a try!)
<div class="header-desc fright"><p><img src="http://myhousesforsaleindetroit.com/wp-content/uploads/2012/09/contact-us-image.png"
alt="Contact us by telephone: (248)468-1598" /></p></div>
As for the image stretching, it looks fine as of right now on the live website, but if you wanted to change the dimensions of it still, a simple photo editor could scale the image down and/or you could specify its dimensions directly to the browser with the width and height attributes.
is a completely free, lightweight -yet quite powerful - photo manipulation program that supports more image filetypes than you can shake a stick at. Load the image in gimp>right click image>image>scale image> (adjust dimensions to fit the div properly and/or stylishly).
Edit: not all browsers display the alt's text, but you would be doing your due diligence to put it in there anyway.