Slow growth across commercial and consumer segments saw sales of players like Apple, Asus and Amazon also falling.
Phablets have screen size ranging from 5-7 inches.
According to preliminary data from IDC, the tablet and 2-in-1 (tablets with detachable keyboards) saw a sequential decline of 35.7 per cent from the high-volume holiday quarter (October-December), and just 3.9 per cent growth over the same period a year ago.
Total shipments were at 48.6 million units in Q1, 2013.
The slowdown was felt across operating systems and screen sizes and likely points to an even more challenging year ahead for the category, IDC said in a statement.
"The rise of large-screen phones and consumers who are holding on to their existing tablets for ever longer periods of time were both contributing factors to a weaker-than anticipated quarter for tablets and 2-in-1s," IDC Program Vice President, Devices and Displays, Tom Mainelli said.
In addition, commercial growth has not been robust enough to offset the slowing of consumer shipments, he added.
Though Apple maintained its lead, its shipment fell to 16.4 million units in the first quarter from 19.5 million units in the year-ago period. Its market share also fell from 40.2 per cent in Q1 2013 to 32.5 per cent in Q1 2014.
Samsung continued to grow its share, increasing from 17.5 per cent to 22.3 per cent this quarter. Its sales stood at 11.2 million units, up from 8.5 million units during January-March 2013.
Asus shipped 2.5 million units (five per cent market share), Lenovo 2.1 million units (4.1 per cent) and Amazon.com one million units (1.9 per cent).
"With roughly two-thirds share, Android continues to dominate the market," Jitesh Ubrani, Research Analyst, IDC Worldwide Quarterly Tablet Tracker said.
Although its share of the market remains small, Windows devices continue to gain traction thanks to sleeper hits like the Asus T100, whose low cost and 2-in-1 form factor appeal to those looking for something that's 'good enough', he added.