Can i upgrade my iCloud storage for my phone, from my computer?

Yes.

If you have a Windows PC:

1. Open iCloud for Windows.
2. Click Storage.
3. Click Change Storage Plan.
4. Choose a plan, then click Next.
5. Enter your Apple ID password, then click Buy.

If you have a Mac:

1. Choose Apple menu  > System Preferences, then click Apple ID.
2. Click iCloud.
3. Click Manage in the bottom-right corner.
4. Click Change Storage Plan or Buy More Storage, and choose a plan.
5. Click Next and enter your Apple ID password.

Source and more information - Upgrade to iCloud+ – Apple Support (UK)