Consumers are buying more on smartphones and cannibalizing some of the purchases that they would have made on tablets. Part of that, is due to the popularity of larger smartphone screens, says Susan Wu, senior forecast analyst for Forrester Research Inc.

“Smartphones are driving a lot of the mobile growth today, especially as retailers make better smartphone interfaces and checkout easier,” Wu says. “Phablets are also putting the pressure on tablets.” Phablets is a term for large smartphones with screen sizes teetering somewhere between a traditional smartphone and a tablet. Indeed the Samsung Galaxy Note 4 phone, for example, boasts a 5.7-inch screen and the iPhone 6 Plus screen measures 5.5 inches. By comparison, the screen size of the iPhone 6 is 4.7 inches. And the iPad offers a 9.7-inch screen and the iPad Mini a 7.9-inch screen.

Consumers who have larger phones also tend to spend more time on the web with their smartphones, as larger screens making it more inviting to watch videos, read articles and do other things. And more smartphone Internet time leads to more shopping, Wu says. “You do see those who have bigger phones making more frequent purchases,” she says.

Online retailer Shop.com, No. 254 in the Mobile 500 Guide, notes a marked decrease in purchases from tablets over the past year. “Sales made using an iPad for sure have slowed,” says Steve Ashley, vice president of mobile and social for Shop.com. Tablets sales, he says, used to account for 75% of total mobile sales with Apple Inc. iPads representing 95% to 96% of that for Shop.com. Today, tablets represent 65% of mobile sales. “We have seen growth in sales from the Microsoft Surface but the rest is migrating to buying on the phones,” he says, referring to the Microsoft tablet. “I can say personally since I bought an iPhone 6 that I do almost all my activities on it and the only time I pull out my iPad is to play a video game.”

Smartphones accounted for 64.1% of all mobile device purchases made via a browser in Q2, up from 61.8% last quarter, according to the Mobile Payments Index from payments vendor Adyen. The index does not track mobile app purchases. “Smartphones are available all the time for shoppers, and (shoppers) can quickly make a purchase as the need arises,” says Kamran Zaki, president of North America, at Adyen “People generally use tablets at certain times of the day, for instance in the evenings after they get home from work.”

Follow mobile business journalist Katie Evans, editor, at Mobile Strategies 360, @Mobile360Katie

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