The phrase "increased steeply" is correct and usable in written English.
It is often used to talk about a sharp or rapid increase, usually in the context of numbers or measurements. For example: "Sales increased steeply in the final quarter of the year."
However, beyond 200 eV, surface roughness increased steeply.
Ongoing violence throughout 2005 increased steeply at year's end and worsened considerably the following year as instability and warfare spread.
Prices increased steeply, then dipped sharply from 1998 to 2001 because of an economic crisis in Russia.
For example, while Americans have gradually decreased the proportion of calories they get from fat over the past few decades, rates of obesity have increased steeply.
Home visits have increased steeply in recent years, particularly in cities, where apartment dwellers struggle with pet conflicts in cramped quarters and without backyard space.
Anti poverty campaigners have lobbied MPs to curtail the power of the banks to raise charges, which have increased steeply in recent years.
Consumer prices had increased steeply in January, following a cold spell in December that cut supplies of produce and reduced fuel oil supplies.
Immediately afterwards, the proportion of articles with open data increased steeply, and by October 2015, 38% of articles in Psychological Science had open data.
The number of single black women bearing children has increased steeply, rising to 415,213 in 1996, from 215,100 in 1970.
Moreover, oxygen reduction current increased steeply with a steady-state current density achieved at high potential (≈ 500 mV), close to the onset potential of oxygen reduction (≈ 580 mV).
Although premiums for such insurance increased steeply after Enron's collapse, they fell by 10% this year, according to a recent survey by Tillinghast, a financial consultancy.
