Phillips Petroleum Co. stock rose by 1 1/2 to close at 47 1/2 today amid rumors that a group led by Pennzoil Co. Chairman J. Hugh Liedtke is about to announce a takeover bid for the company. Phillips was the second-most-active stock on the New York Stock Exchange as 2.5 million shares were traded.

Late last month, Phillips defended itself against a takeover bid by agreeing to purchase a block of stock owned by Mesa Partners, a group led by Mesa Petroleum Co. Chairman T. Boone Pickens Jr. Since that time, Phillips stock dropped from a high of 56 1/4 to the low 40s, angering professional Wall Street investors who had purchased stock in anticipation of a quick profit.

The scenario discussed most often today involves two Wall Street investors, Ivan Boesky and Carl Icahn, in addition to Pennzoil. Boesky and Icahn each reportedly own several million Phillips shares and are cooperating with Pennzoil, which has about $3.5 billion available to make a bid for Phillips.

One year ago, Pennzoil became involved in a similar takeover battle when it made a tender offer for Getty Oil Co., which later was purchased by Texaco Inc.

Phillips stockholders are supposed to vote on a restructuring plan in late February or early March that would replace about one-third of the company's common stock with several billion dollars of debt. The plan, devised in connection with the aborted Mesa takeover bid, also calls for the establishment of an Employe Stock Ownership Plan that would purchase 32 million Phillips shares.

Many Wall Street professionals are unhappy with the plan and would favor an alternate buyout bid.

Other companies mentioned today as possible Phillips suitors included Royal Dutch/Shell and Occidental Petroleum Corp.

"The way I see it, some [arbitrageurs], including Boesky and Icahn, were hurting in their investment and have gotten together," said Alan Edgar, an oil industry analyst with Schneider, Bernet and Hickman Inc. in Dallas. "The name that makes the most sense is Liedtke [Pennzoil] since he has the dollars and wants to do it."

There was no comment yesterday from Boesky, Icahn, Pennzoil or Phillips.