I installed Joomla 2.5.1 and Phoca Gallery 3.1.5 once again in a new root.
Options works fine now but there another problem occurred!
If I load an new image in a category, only the medium thumbnail is created and the image doesn't appear in the images list. It happens in both cases Jfile thumbnail creation on and off
If you upload all images in a folder first and the assign the images 1 by 1 to a category, the small , medium en large thumbnails are generated!
If you want to assign an image to a category and the image is not in the folder yet
then after uploading only the medium thumbnail is generated and no record is written in the databse in which the assignment is stored
For now the problem is solved I can continue.
I'm going to check the PHP settings later