What if I lost my iPhone can I access its photos using icloud

If you were using iCloud Photos, you can download the photos onto a computer. Take a look at this.

Archive or make copies of the information you store in iCloud - Apple Support

If you were backing your photos up with iCloud, rather than using iCloud photos, the only way to recover the photos would be to restore the backup to another iOS device.

Perhaps, this would be helpful for the loss of the phone.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support