are my iCloud photos stored? I lost phone abroad and want to access the photos and save them to my iPad.

Photo stream photos remain in iCloud for 30 days, and can be accessed by enabling my photo stream on another iOS device or computer. Shared streams remain in iCloud indefinitely, and can be accessed by enabling Photo Sharing on an iOS device or computer. Your camera roll photos are included in your device backup. Restoring the backup to another iPhone or iPod touch should recover them (unfortunately, you can recover them by restoring an iPhone backup to your iPad). If the backup is an iCloud backup be aware that Apple will delete it after 180 days of inactivity so you'll want to restore the backup prior to that.

Are you sure they were all in your my photo stream? My photo stream only maintains a rolling collection of your last 1000 photo stream photos, not 4000. And depending on when you first enabled my photo stream on your iPad, it may not have downloaded all the photo stream photos that were on your phone at the time. iCloud only keeps photo stream photos for 30 days, giving your devices enough time to download them. When you first enabled it on your iPad you would only have been able to download photos from the last 30 days, even though you may have had old photo stream photos on your phone.