If you are talking about web bookmarks in the Safari app, the only way to arrange bookmarks alphabetically is for you to manually arrange them that way. To do:
1) Press on the icon that looks like an open book. You'll get a little drop down box.
2) Press the Edit button (top right of the drop down) and you will see three light gray lines appear next to your bookmarks.
3) Press and hold any one of those three gray line areas and this will allow you to move that bookmark around.
Once you are done moving your book marks to where you wish, press the blue Done button and that's it, you are finished.
I apologize if you already knew this, but this is the only way you can organize your book marks. Good luck and I hope this helps.
Marilyn