Credit Karma gives you a Vantage score, Goldman was almost certainly giving you a FICO score, and vantage skews more towards people who are building/rebuilding credit.
As for the credit dip after you bought your phone, it’s possible you bought it the one day between billing cycles that your card reports to the credit agencies. Let’s say your billing cycle is the 11th through the 10th and payment is due on the 5th of the following month. Your credit card company would probably report on the 11th or 12th, after the close of the billing cycle. So if you bought your phone at the start of the billing cycle and paid it off the next day, it’s possible it was in that 24 hours that your monthly balance was reported to the credit bureaus and the zero balance wouldn’t be updated with the credit bureaus until the following month when they updated again.