Apple’s flirtation with $1 trillion may be distracting investors from a big challenge: Can customers stomach continued price increases for its iPhone?

Investors were impressed when Apple reported earnings for its fiscal third quarter, or the three months through June, on Tuesday. The company’s stock jumped nearly 6 percent on Wednesday and pushed its market value to nearly $973 billion.

Apple sold only 1 percent more iPhones, by far its main source of revenue, than a year earlier. But revenue from iPhones surged 20 percent from a year earlier because their average selling price rose 20 percent.

The positive spin was that Apple was able to keep its sales price up. Customers, it seems, are willing to pay $1,000 or more for the iPhone X, released at the end of 2017.

The average iPhone price usually drops as the selling cycle progresses. That is happening this year, but the decline has not been as steep. The $724 average price in Apple’s third quarter was 9 percent below the $796 average in the company’s first quarter (the fourth quarter of 2017). That was less than the 13 percent decline after the iPhone release at the end of 2016.

And the company’s revenue forecast suggests that the iPhone’s financial performance is not about to disappoint in the current quarter.

What’s not to like about this situation? Apple may not be able to get away with such a large price increase when it releases its new phones at the end of this fiscal year. When the current batch of iPhones was released, Apple hoisted its average iPhone price by 29 percent, by far the highest increase of the past five releases. In other words, there may not be much headroom left for further hikes, especially since the new iPhones are not expected to be substantially different from the current models.

Jeffrey Kvaal, an analyst at Nomura, forecasts that the average iPhone price will rise only 3 percent in Apple’s 2019 fiscal year, compared with 15 percent for all of its 2018 fiscal year.

Of course, if Apple does try to charge a lot more, it may sell fewer iPhones, denting revenue as a result. And iPhone sales in China, a huge and growing market for Apple, will be at risk if a full-blown trade war with the United States breaks out and Chinese consumers pull back as a result.

Apple makes so much money that it can ride out underwhelming iPhone cycles. Investors, however, have in the past soured on Apple’s stock when its iPhones fail to excite and revenue fails to match investors’ high expectations. So far, selling expensive iPhones has kept Apple’s profits surging and pushed its valuation within spitting distance of $1 trillion. But the strategy may not have staying power, and Apple could just as easily stumble after it has passed that milestone.