Your page is "responsive". As you can see, things shift around when you resize the browser.
The problem is, it's not done correctly. Don't get defensive yet.
The problem is you've hardcoded margins and paddings in your CSS... which may look fine when you're previewing your site on a wide monitor... but these hardcoded margins and paddings will not work/or the values are not applicable anymore when your site is viewed using a different window dimension.
For example, on your logo you have a hardcoded padding-left: 150px;
A phone is only around 320px wide... right there, that padding is already eating a big chunk of your phone real estate.
If you need to use hardcoded values like this on a design (for tighter control of your layout), then you need to use @media-queries so you can also designate new/adjusted values for these hardcoded values on different size displays.
Here's more info on media queries.
Your images need to have some classes too, otherwise, they remain a fixed dimension regardless of your browser/window size. See img and img-responsive bootstrap classes. You're using V3 bootstrap, so this is the reference for it