In contact form shortcode you can set set web url and phone parameter value as “false”.(Pls check contact form shortcode in themedocumentation)
Or You can apply custom CSS in themeoptions to hide the specific fields.
Currently we have set same width for text input fields so if we will change the width for subject field which is a text input field will automatically reflect the name and email field, otherwise you need to assign an id for subject field and then you will be able to apply custom CSS only for that particular field.