I'm sorry to hear that you are having difficulties with Juicebox-Pro.
Hopefully my notes below will help.
I have tried many different ways to make my Juicebox gallery to be responsive to all devices.
As your gallery is a 100% x 100% gallery with no other content on the web page, your gallery (but not necessarily the main image being displayed within the gallery) should completely fill the browser window.
No matter what size the gallery is, the main images within the gallery will be scaled according to the value of the imageScaleMode configuration option.
Please see the entry for imageScaleMode in the Main Image section of the Config Options page for short descriptions of the possible values (SCALE_DOWN, SCALE, FILL, STRETCH, NONE).
Your gallery uses the default value for imageScaleMode (SCALE_DOWN) so images will be scaled down (if necessary) to fit within the gallery's image area (after space has been reserved for other gallery elements such as the caption, thumbnail and TOP areas) without cropping or stretching. Small images will not be scaled up so, in a very large browser window, the images may be displayed at their actual size with space surrounding them. In such a scenario, you could instruct Juicebox-Pro to scale up small images (by setting imageScaleMode="SCALE") but their visual quality may decrease and a better solution is usually to provide larger gallery images (in terms of resolution).
These settings change the size of the boundaries around the image when viewed on computer but not on phones.
Your gallery uses stagePadding="20". This is a Large Screen Mode Option only (noted in the General section) so there will be 20px of space surrounding the gallery on all sides in Large Screen Mode (desktop browsers) but not in Small Screen Mode (on mobile devices). Other configuration options may also be Large Screen Mode only so please check the Config Options page for details.
I want the full image to be seen not cropped and not stretched.
I do not have an iPhone 6 but I have viewed your gallery in Mobile Chrome and Mobile Safari on an iPod Touch 6 running iOS 11.4.1 and everything looks as expected. All your images are displayed in full with their aspect ratios respected (with no cropping or stretching).
I notice that your gallery uses Juicebox-Pro v1.5.0.
Please try upgrading to the latest version (v1.5.1) to see if this helps with your problem. Many bugs have been fixed since v1.5.0 (please see the Version History page for details) and upgrading may fix your problem without any further action.
Full instructions for upgrading JuiceboxBuilder-Pro and existing galleries can be found on the Upgrading Juicebox support page.
Essentially, all you need to do to upgrade your gallery is to swap its existing 'jbcore' folder with the 'jbcore' folder from the Juicebox-Pro v1.5.1 zip package ('juicebox_pro_1.5.1/web/jbcore/').
After upgrading your gallery, please clear your browser's cache to ensure that your browser is using the latest versions of your gallery files from your web server (instead of cached versions).
If, after upgrading your gallery, you still see the problem, please let me know what browser(s) you see the problem in and what version of iOS your iPhone 6 is running.
If possible, please also provide a screenshot (you can attach an image to a post here in the forum or upload it somewhere and provide a link) so that I can see what you are seeing.
Thank you.