I just checked your site (the homepage) on a mobile device and the logo is responsive (it is smaller).
The problem i actually the width of the Submit button in the contact section.
Look at line 1217 of your style.css file. The width is 40em.
Change that to something smaller for mobile phones in the media queries at the bottom of the style.css file.
Or remove the width attribute.
That is causing your page to be larger than the screen width on mobile devices. Which is affecting your logo.