That is a very large backup (4.58 GB) for a single iPhone, which usually indicates that you are carrying around a lot of photo & video taken with your iPhone's camera. Photo & video you take with your iPhone get saved in its "Camera Roll" album, which is its on-board storage. I suspect that you are carrying around a few GB's worth of photo and/or video in your Camera Roll, which is making your backup HUGE. If you go to your iPhone's Settings > General > Usage > Manage Storage > Photos & Camera you can see how much space is being taken up by your photos and videos in your "Photo Library", I bet it is a lot. The "Photo Library" is the only part of photo storage that is part of your backup, other categories like "My Photo Stream" and "Shared Photo Stream" are not part of your backup.
A couple options for you if indeed your Camera Roll (i.e. Photo Library) is a few GB in size:
1- Reduce On-Board Storage:
If you have not done so already, use photo managing software on your Toshiba to copy your photos and videos from Camera Roll to your laptop's hard drive. Your PC came with "Microsoft Camera and Scanner Wizard" which should see your iPhone as a digital camera. Use that (or other similar software) to copy all items or just the ones you want to save. Your PC may also have other Microsoft applications like Microsoft Live Photo Gallery, or Office Picture Manager, and most of these utilities give you the option to delete the items from your "camera" once the items are copied to your computer -- this is important, because you want to slim-down your iPhone's Camera Roll.
Once you save the photos & videos that you want saved to your Toshiba, if you have not deleted them from your iPhone you can do so manually, one at a time, or as noted above use the photo manager software to delete the items once copied to your computer.
Now check your on-board storage on your iPhone in the Settings as above and see if it has gone down, then your next device backup ought to be much smaller (and faster to complete).
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2- Change Your Backup Location:
Instead of backing your iPhone up to iCloud, change its settings to back up to your computer (via iTunes). You can then delete your iCloud backup if desired, and just rely on your local (iTunes) backup if/when needed. The caveat is, make sure your Toshiba has plenty of storage space for this backup, and backup to your Toshiba "often" (I backup daily, takes only seconds in my case). BUT, even if you go this route, you really ought to reduce your Camera Roll as above if you're carrying around so many photos & videos.
