You should not run into any problems using the quotation on t-shirts. You're correct that copyright doesn't protect short phrases although that would not be an issue here because nobody is claiming authorship of the quote. Note that a variation on the phrase was popularized (and sometimes attributed to) Bella Abzug.
You are also okay because nobody has sought to assert trademark rights to the phrase. Curiously, in 2010 an applicant from California applied to the USPTO to register the phrase, "A Woman Belongs in the house the White House the House of Representatives the House of Congress the House of the Senate the Mayor's House the Governor's House the Courthouse" on caps and t-shirts. The application was approved by the USPTO but abandoned before registration. Similarly, a 2007 application for A Woman's Place ... is in the White House" was approved for registration but was abandoned by the applicant.