Karma + Selenium + Jasmine: Is it possible to specify a browser for it("should...")?

Karma runs our project's tests, and I would like to run some UI tests with karma-selenium-webdriver-launcher.

I notices some example code that looks like this (see original)

var By = require('selenium-webdriver').By,
    until = require('selenium-webdriver').until,
    chrome = require('selenium-webdriver/chrome');

module.exports = function(config) {
    config.set({

        customLaunchers: {
            swd_chrome: {
                base: 'SeleniumWebdriver',
                browserName: 'Chrome',
                getDriver: function(){
                    // example from http://ift.tt/1Mk8RCm
                    var driver = new chrome.Driver();
                    return driver;
                }
            }
        },

        // 'PhantomJS' already works in our configuration. 'swd_chrome' is the new thing we want to use...
        browsers: ['PhantomJS', 'swd_chrome'],

    });
};

How do I specify that most tests (ie. unit tests) should only be run in Phantom while others (ie. UI tests) should run chrome?