您可以使用phonegap中的FileReader对象检查文件是否存在。您可以检查以下内容：

var reader = new FileReader();
var fileSource = <here is your file path>

reader.onloadend = function(evt) {

    if(evt.target.result == null) {
       // If you receive a null value the file doesn't exists
    } else {
        // Otherwise the file exists
    }         
};

// We are going to check if the file exists
reader.readAsDataURL(fileSource);