My Galaxy Tab 3 requires a cable so what can I use as a substitute? Is it ok for me to charge my galaxy tab 3 using a samsung phone charger?(only the cable is from the phone, the jack is of the tab)
If your using the charger that came with the tablet it doesn't matter really.

You can use any charger if you want but it may lead to damage to the battery if you overcharge it. But the cable doesn't make a diffrence.