On mobile phone I see only thumbnails and main image is displayed only when I client on thumbnail.
What you are describing is Small Screen Mode.
On mobile (small screen) devices, Juicebox displays the gallery in Small Screen Mode where the thumbnails and main images are displayed on separate pages (to give the main images as much room as possible to be displayed).
When a thumbnail is clicked/tapped, the thumbnail page is replaced with the chosen image.
The user can return to the thumbnail page by clicking/tapping the 'Thumbnail' button on the gallery's Button Bar.
Please see the Screen Modes support section in the Gallery Tour for more information.
You can choose to always have the gallery displayed in Large Screen Mode (which displays the thumbnails and image images together, like in a desktop browser, no matter what device the gallery is viewed on) by setting screenMode="LARGE" (in JuiceboxBuilder-Pro's 'Customize -> General' section).
If you would like to continue to use Small Screen Mode for mobile devices but would rather have the first image displayed initially rather than the thumbnail page, then set showSmallThumbsOnLoad="FALSE" (in JuiceboxBuilder-Pro's 'Customize -> Thumbnails' section).
Also, if you would like to have your web page's content (including the thumbnails and Button Bar) scaled up when displayed on mobile devices, then try adding the following <meta> tag to the <head> section of your gallery's web page:
<meta name="viewport" id="jb-viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1, maximum-scale=1, user-scalable=0" />
I hope this helps.