You can set the question text type to Multi Line or Essay Text Box. Either of these options will increase the size of the text box when you publish it. You can also grab the bottom right corner of the text box to expand it to a size that is better for you. More information can be found in this article:
https://www.qualtrics.com/support/survey-platform/survey-module/editing-questions/question-types-guide/standard-content/text-entry/