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.
To use a charger for your device, see the following requirements:
1- The charger plug should fit into your device.
2- The charging source should voltage should be the same in type (DC or AC) and required voltage by your device should be the same as provided by the charger EX: 5V DC Output from charger should be 5V DC input to device.
3- The charger current (measured in Amperes) should be more equal or greater than the required current by your device, EX: device requires 2A the charger should have 2A or greater.
1-Use the charger provided by your manufacturer.
2- Use the above instructions at your own risk.